The present invention relates to a device for cutting a continuous paper and included in a thermal printer and, more particularly, to a continuous paper cutting device for a thermal printer of the type conveying a continuous paper by rotating a platen formed of an elastic material having a great coefficient of friction.
A thermal printer of the type described has a thermal head and a platen facing the head and formed of an elastic material having a great coefficient of friction. The platen is driven by a stepping motor via a gearing so as to convey a continuous paper. The head is constantly biased toward the platen by a spring and is pivotally movable about a fixed shaft away from the platen against the action of the spring. The continuous paper is received in a storing section located upstream of the platen in the intended direction of paper transport. Perforations are formed in the paper at predetermined intervals in order to facilitate the separation of the paper. The paper is payed out from the storing section to between the head and the platen and conveyed by the platen. A sensor responsive to the consecutive perforations of the paper is located between the platen and the storing section.
An upper and a lower cutter, each having a sharp edge, are positioned downstream of the platen in the direction of paper transport. After an image has been printed on the leading part of the paper by the head and platen, the paper is brought to a stop when the peforation immediately following the printed part reaches the upper and lower cutters. On sensing the above perforation, the sensor outputs a signal for causing it to be accurately stopped at the cutters.
To cut the paper, the operator pulls the paper, stopped at the above position, either obliquely upward or obliquely downward. Because the paper has its trailing portion nipped by the head and the platen, it is cut along the perforation by the sharp edges of the cooperative cutters. Subsequently, the paper is again conveyed until the first print line of its trailing portion arrives at the head. In this position, the paper waits for the next printing operation.
A problem with the conventional continuous paper cutting device is that the sharp edges of the cutters sequentially wear due to repeated cutting. Therefore, the cutters must be replaced periodically. Because a preselected format is printed on each of the consecutive sheets of the continuous paper divided by the perforations, an image must be accurately printed within the frame of the format. Hence, if the perforation of the paper is not accurately stopped at the edges of the cutters, then the paper will be cut or torn off at a position other than the perforated portion. To obviate this occurrence, it is necessary to accurately control the distance between the thermal head and the sensor responsive to a detection of the perforation and due concern for the distance between the edges of the cutters and the above sensor. Or, it is necessary to use two sensors responsive to the printing position and the cutter position, respectively. This results in a complicated construction and control. Moreover, because the related parts must also be provided with high accuracy, the production cost of the printer increases. Should the perforation fail to meet the cutters accurately, the paper would be cut at an unexpected portion other than the perforation.